What does Genesis 21:11 mean?

The language of this short verse indicates that Abraham expressed great emotion. He was very displeased with Sarah's sudden demand to cast out his firstborn son, Ishmael. The word "displeased" is not often used in the Old Testament and only to express great anger. Abraham was very displeased.

Clearly, Abraham loved Ishmael. When God revealed that Isaac would be born within a year's time, Abraham had immediately mentioned his wish that Ishmael could live before God (Genesis 17:18). God had assured Abraham that Ishmael would be greatly blessed, but that the covenant would pass through Isaac.

Sarah, on the other hand, is expressing a similar level of anger and bitterness as she did earlier in Ishmael's life (Genesis 16:4–6). She claims to be concerned that Ishmael will interfere with Isaac's inheritance. That's not completely unreasonable, since Abraham is obviously attached to his teenaged son.

Despite Sarah's insistence, Abraham would not likely have let Ishmael go if the Lord had not instructed him to do so in the following verse. This instruction comes along with an assurance, from God, that Ishmael will be blessed.